PURPOSE: To provide an optical element module which has no instability of an operation due to dew-condensation and a long life, in which performance is improved and which is adapted for an OTDR. CONSTITUTION: An optoelectronic component 10 which generates heat such as an avalanche photodiode, a laser diode, etc., and a temperature controller 12 thermally coupled with a heat absorber such as a Peltier element 11, etc., are provided, and so connected to a heat sink as to be thermally conducted. Further, they are enclosed in an airtight package and a dry gas atmosphere is provided. COPYRIGHT: (C)1993,JPO&Japio